1. Field of the Invention
The invention relates to a signal transmission circuit of a wireless telephone handset, and more particularly, to a signal transmission circuit of a wireless telephone handset for reducing power consumption.
2. Description of the Prior Art
A battery is typically used to supply power to a wireless telephone handset. Unfortunately, there are certain problems associated with using batteries. First of all, batteries may weigh down the telephone handset if they are not made light and compact. Also, the power supplied by a battery is often limited. Another consideration is the sensitivity of the handset. Reducing handset power consumption and increasing handset sensitivity has become the recent focus of handset design.
Please refer to FIG. 1. FIG. 1 is a perspective diagram of a prior art signal transmission circuit 10. The signal transmission circuit 10 is used in a wireless telephone handset. The signal transmission circuit 10 comprises a voice transformation circuit 12 for transforming a user""s voice into a voice signal, a voice modulator 14 electrically connected to the voice transformation circuit 12 for modulating the voice signal and transforming it into a radio frequency signal, a power amplifier 16 electrically connected to the voice modulator 14 for amplifying the radio frequency signal, an electric source 22 electrically connected to the power amplifier 16 for supplying power to the power amplifier 16, an antenna 20 for transmitting the radio frequency signal outputted from the power amplifier 16, and a matching circuit 18 electrically connected between the power amplifier 16 and antenna 20 for matching the impedance of the power amplifier 16 and antenna 20.
When the handset is outputting or receiving signals, the power amplifier 16 is always switched on. When the handset is outputting the user""s voice signals, the power amplifier 16 amplifies the radio frequency signal generated by the voice modulator 14, and the radio frequency signal is outputted through the antenna 20. When the handset is receiving signals, the power amplifier 16 is still switched on so as to consume power. Because the electric source 22 continuously supplies power enabling the power amplifier 16 to remain on, the power is easily consumed. This shortens the life span of the battery of the handset. Also, in the prior art signal transmission circuit 10, w hen the handset is changed from outputting signals to receiving signals, timing error may occur which causes undesired signals to be amplified by the power amplifier 16 and leads to unnecessary power consumption of the handset. Finally, received signals may not be properly detected so the sensitivity of the handset will be reduced.
It is therefore a primary objective of the present invention to provide a signal transmission circuit of a wireless telephone handset for reducing power consumption and improving the sensitivity of the handset.
Briefly, in a preferred embodiment, the present invention provides a signal transmission circuit of a wireless telephone handset comprising:
a voice transformation circuit for transforming a user""s voice into a voice signal;
a voice modulator electrically connected to the voice transformation circuit for modulating the voice signal and transforming it into a radio frequency signal;
a power amplifier electrically connected to the voice modulator for amplifying the radio frequency signal;
a first switch electrically connected to the power amplifier for turning the power amplifier on and off;
an antenna for transmitting the radio frequency signal outputted from the power amplifier; and
a control circuit for controlling operations of the telephone handset;
wherein when the telephone handset is transmitting the radio frequency signal using the antenna, the control circuit turns on the power amplifier by using the first switch so that the radio frequency signal generated by the voice modulator can be amplified by the power amplifier and then be transmitted through the antenna, and when the telephone handset is receiving a radio frequency signal, the control circuit turns off the power amplifier by using the first switch to reduce power consumption.
It is an advantage of the present invention that when the handset is receiving a radio frequency signal, the control circuit uses the first switch to turn off the power amplifier and the second switch to prevent interference. Therefore, the power consumption of the handset using the signal transmission circuit is reduced and the sensitivity of the handset is enhanced.
These and other objects and the advantages of the present invention will no doubt become obvious to those of ordinary skill in the art after having read the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings.